BIT 115: Introduction To Programming Professor: Dr. Baba Kofi Weusijana Pronounced Bah-bah Co-fee Way-ou-see-jah-nah Call him “Baba” or “Dr. Weusijana”

Lecture 8 Log into Canvas Put your name sticker on your computer Announcement: Java Code Critic Feedback Quiz08 Printing to output ICE08 Returning Quiz04

Java Code Critic Feedback A1 and ICE07 critiques of Java code are done So you can start work on A1 revisions! Lots of red comments doesn't necessarily mean your code is worse Generally your grade and overall comments indicates how well you did For ICE07 you got 10 points if you simply turned it in on time, so look for a Java Code Critic grade of “Well Done!” to indicate you have very little to worry about Often I’m commenting on coding techniques I have not lectured on yet (and thus might not be relevant to the midterm) Many critiques are about code conventions They are very important because they help you and other programmers understand and maintain your code but they usually don’t affect how computers will run your application Ask questions about requirements (even during exams)! It is better to get critiques about your coding Critiques about you not following instructions are not as useful toward helping you to learn coding BIT 115: Introduction To Programming3

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And Now… Sit Next To Each Other

Chapter 6.6.1: Output (Printing Text Messages To The Screen) Info we get from the user is input Either from the keyboard, mouse, or something else like a network connection or other type of cable We will be looking at input after the midterm Info we show to the user is output This can be a message, additional information, even a request that the user perform some kind of action These messages and information are typically “hard-coded” into the program itself, then pushed out to the screen, console, or monitor using specific print-to-the-screen mechanisms (services) that are a part of Java

The Console Window The console window that starts a Java application is typically known as the standard output device. The standard input device is typically the keyboard. Java sends information to the standard output device by using a Java class stored in the standard Java library. In jGRASP, this output is displayed in the Run I/O tab In Eclipse, this output is displayed in the Console tab Java classes in the standard Java library are accessed using the Java Applications Programming Interface (API). The standard Java library is commonly referred to as the Java API.

“Hello World!”

The Console Window Example: System.out.println("Programming is great fun!"); This line uses the System class from the standard Java library. The System class contains methods and objects that perform system level tasks. The out object, a member of the System class, contains the methods print and println.

The Console Window The print and println methods actually perform the task of sending characters to the output device. The line: System.out.println("Programming is great fun!"); is pronounced: System dot out dot printline The value inside the parenthesis will be sent to the output device (in this case, a string). The println method places a newline character at the end of whatever is being printed out. The following lines would be printed out on separate lines since the first statement sends a newline command to the screen: System.out.println("This is being printed out"); System.out.println("on two separate lines.");

The Console Window The print statement works very similarly to the println statement. However, the print statement does not put a newline character at the end of the output. The lines: System.out.print("These lines will be"); System.out.print("printed on"); System.out.println("the same line."); Will output: These lines will beprinted onthe same line.

The Console Window For all of the previous examples, we have been printing out strings of characters. Later, we will see that much more can be printed. There are some special characters that can be put into the output. System.out.print("This line will have a newline at the end.\n"); System.out.print("This doesn’t show up on the same line."); The \n in the string is an escape sequence that represents the newline character. Escape sequences allow the programmer to print characters that otherwise would be unprintable.

Java Escape Sequences ("Special Characters") \n newlineAdvances the cursor to the next line for subsequent printing \t tabCauses the cursor to skip over to the next tab stop \b backspaceCauses the cursor to back up, or move left, one position \r carriage return Causes the cursor to go to the beginning of the current line, not the next line \\ backslashCauses a backslash to be printed \'\' single quoteCauses a single quotation mark to be printed \"\" double quoteCauses a double quotation mark to be printed

Even though the escape sequences are comprised of two characters, they are treated by the compiler as a single character. System.out.print("These are our top sellers:\n"); System.out.print(“==========================\n"); System.out.print("\t- Computer games\n\t- Coffee\n "); System.out.println("\t- Aspirin"); Would result in the following output: These are our top sellers: ========================== - Computer games - Coffee - Aspirin With these escape sequences, complex text output can be achieved. Java Escape Sequences ("Special Characters")

The + operator can be used in two ways. (1) as a concatenation operator (2) as an addition operator If either side of the + operator is a string, the result will be a string. System.out.println("Hello " + "World!"); Hello World! System.out.println("The value is: " + 5); The value is: 5 System.out.println("The value is: " + value); The value is: System.out.println("The value is" + ": \n" + 5); The value is: 5 The + Operator

String Concatenation Java commands that have string literals must be treated with care. A string literal value cannot span lines in a Java source code file. System.out.println("This line is too long and now it has spanned more than one line, which will cause a syntax error to be generated by the compiler. "); The String concatenation operator can be used to fix this problem. System.out.println("These lines are " + "now ok and will not " + "cause the error as before."); String concatenation can join various data types. System.out.println("We can join a string to " + "a number like this: " + 5);

String Concatenation The concatenation operator can be used to format complex String objects. System.out.println("The following will be printed " + "in a tabbed format: " + "\n\tFirst = " + 5 * 6 + ", " + "\n\tSecond = " + (6 + 4) + "," + "\n\tThird = " "."); Notice that if an addition operation is also needed, it must be put in parenthesis.

Printing as Part of Program Decision- Making int newNum = 3; if( newNum >= 5 ) { System.out.println( newNum + “ is larger than 4”); } else { System.out.println( newNum + “ is smaller than 5.”); } Basic Output Demo.java Demo: Two Points: 1) ‘+’ for concatenation 2) spaces in “ ”double-quotes

In-Class Exercises ICE08: Output (Printing Text Messages To The Screen)

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